1. Field of the Invention
The present invention relates to a method for measuring a higher-order mode cutoff wavelength of an optical fiber and to an optical communication system using the method.
2. Description of the Related Art
It is important that an optical fiber used as an optical transmission path in an optical communication system have a single mode at a signal light wavelength (or a higher-order mode cutoff wavelength is shorter than a signal light wavelength). As methods for measuring a higher-order mode cutoff wavelength of an optical fiber, IEC 60793-1-44 (JIS C 6825) describes the bend reference technique (60793-1-44© IEC: 2001 p. 27) and the multimode reference technique (60793-1-44© IEC: 2001 p. 27). However, with the bend reference technique or the multimode reference technique, it may be difficult to measure cutoff wavelengths of the following optical fibers:
an optical fiber having low bending loss in higher-order modes (see Fujikura Giho, No. 105, pp. 6-10 (2003) M. Ikeda, et al.);
an optical fiber having a plurality of higher-order mode cutoff wavelengths close to each other; and
an optical fiber having a cutoff wavelength close to an OH induced loss wavelength.